The present application relates to a recording and reproducing apparatus that records data in and reproduces the data from a hologram recording medium in which the data is recorded by an interference fringe between reference light and signal light and a method of recording and reproducing the data. The present application also relates to a reproducing apparatus that reproduces data from the hologram recording medium and a method of reproducing the data.
In a hologram recording and reproducing system and, in particular, a hologram recording and reproducing system in the field of optical storages, for example, a transmission liquid crystal panel and an SLM (spatial light modulator) such as a DMD (Digital Micromirror Device: registered trademark) are used for light intensity modulation. Intensity modulation for obtaining pattern arrays of bit 1 (e.g., light intensity is high) and bit 0 (e.g., light intensity is low) is applied to signal light.
In the SLM, for example, as shown in FIG. 2, signal light is generated by giving light intensity modulation to the center thereof according to recorded data and reference light is generated by transmitting light in a ring shape around the signal light. The signal light modulated according to the recorded data is irradiated on a hologram recording medium together with the reference light. Consequently, an interference fringe between the signal light and the reference light is recorded on the hologram recording medium as data.
When the data is reproduced, only the reference light is generated and irradiated on the hologram recording medium by the SLM to obtain diffractive light corresponding to the interference fringe. An image corresponding to the diffractive light is focused on an image sensor such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Oxide Semiconductor) sensor to obtain respective values of recording bits and perform data reproduction.
The hologram recording and reproducing system for irradiating the signal light and the reference light on an identical optical axis is known as a coaxial system.
Examples of a related art include “Nikkei Electronics, Jan. 17, 2005, p. 106 to 114”.